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Thread: One of the worst flying days I have had in quite some time
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Old Oct 25, 2011 | 5:55 am
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/dev/null
 
Join Date: Aug 2011
Location: JAN
Programs: DL PM
Posts: 40
Originally Posted by DLdweeb
My first time in coach on an A320 I heard this on final and had no idea what was going on. A pilot friend told me it was the hydraulic system equalizing pressure. Don't know if that's true or not but it is an interesting sound.
It's the Power Transfer Unit (PTU), keeping two hydraulic systems pressurized when only one engine is running. Ordinarily the hydraulic systems connected by the PTU (green and yellow are how they're named, I think) are pressurized by their own engine-driven pump, but when a single engine is running (during taxi, for example) the PTU noisily keeps both sides pressurized.
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